let functions = [
  ( "cubic", (fun x -> x*.x*.x), 0.0, 1.0, 100);
  ( "recip", (fun x -> 1.0/.x), 1.0, 100.0, 1000);
  ( "x to 5e3", (fun x -> x), 0.0, 5000.0, 5_000_000);
  ( "x to 6e3", (fun x -> x), 0.0, 6000.0, 6_000_000)
]